New OPML Features added to MultiMarkdown

For anyone using MultiMarkdown with OmniOutliner or other OPML applications, I
have added additional OPML support to MultiMarkdown.

Specifically it is now possible to “round trip” a document from a plain text
MMD file, to an OPML file containing MMD markup, and back to a plain text file
without corrupting the structure, or the content.

mmd2OPML.pl is used to convert a plain text file into an OPML file

OPML2mmd.pl is used to convert an OPML file into a plain text file

The layout of the OPML file is consistent with the structure expected by my
OmniOutliner export plugin. This
means that the OPML file can be imported into OmniOutliner, and then exported
back as an OPML, or exported directly within OmniOutliner into a MultiMarkdown
text file (with or without attachments). Which brings up the point that the
attachment support is only for OmniOutliner (at least for now).

I’m not sure what other applications are out there that would be useful for
editing MultiMarkdown in an OPML format, but these new tools make it possible.
Alternatively, it may be helpful to temporarily convert a MultiMarkdown text
file into OPML if only to help reorganize the document quickly.

One limitation of this approach is that if you are using a “non-standard”
numbering scheme for your header levels you may find that the structure of the
resulting documents are not what you expect. For example, the “children” of an
h2 level section, will by definition be h3. With plain text files, you can
specify whatever level you like — in other words the level of the header
(h2, h3) had no intrinsic meaning. In an OPML document, they correlate
directly to the levels of the outline, which obviously cannot skip a
“generation”. In my mind, however, this is a feature, not a bug, and will
probably not be changed.

Additionally, I just discovered that not every OPML tool supports a “_notes”
field. OmniOutliner allows you to have a “title” for each piece of the
outline, and a separate notes field that holds the content. It appears that
there is no standard approach to this. So some OPML apps will simply import
the hierarchy of section titles, but no content…. If anyone else uses these
features, let me know if there is a workaround for the app you use…
Unfortunately, it appears that these features may only be useful for
OmniOutliner users…